Cooling things: Difference between revisions
Jump to navigation
Jump to search
| Line 962: | Line 962: | ||
===Windows and windcatchers=== | ===Convection in houses; Windows and windcatchers=== | ||
<!-- | <!-- | ||
| Line 968: | Line 968: | ||
Isolation lessens the absorption, though not so much other concentration. | Isolation lessens the absorption, though not so much other concentration. | ||
Which means that throughout the day, the walls in general, and the air in some rooms, will be warmer than the outside air. | |||
Particularly when evening air gets colder in the day. | |||
In fact, desert areas see some specific designs ''exactly'' because the day/night temperature difference is larger, | |||
and you may have a little more space to work with too. | |||
When opening a window on two sides of the house, combined with a little wind, | |||
creates enough draft that you are replacing the air throughout the day, | |||
then you are moving out the concetrated heat, | |||
and replacing it with whatever the outside air is. | |||
Ideally, houses don't trap heat like that, | |||
but where they do, this can matter a few degrees for free. | |||
Windcatchers refers to one of two or three things, | |||
which all amount to designing for some draft without active machinery. | |||
Few are hugely efficient, but it's passive so it's free. | |||
You can lessen local buildup of heat above ambient, but also that you never go below ambient | You can lessen local buildup of heat above ambient, but also that you never go below ambient | ||
One is using already-present wind to create a draft, as just mentioned. | |||
If you can't count on wind, then putting the windows to the north and south helps a little, | |||
because one heats more than the other, and you get some natural convection. | |||
You can also make what amounts to a chimney, that is directly heated by the sun (so on a sun-facing wall), which heats the air inside that chimney so that it slowly moves upwards (and is never in the home), and that air movement draws in air from whatever other ventilation the house has, usually just outside air through windows and such. | |||
In some circumstances you can do even fancier things. | |||
If you are very lucky and have an underground canal near you, | |||
this is likely to be somewhat colder. | |||
If you also have the space for large towers, you can catch wind, | |||
and blow them over that canal. This is basically larger-scale evaporative cooling, | |||
and in theory you can can cool down air to the temperature of that water. | |||
https://en.wikipedia.org/wiki/Windcatcher | https://en.wikipedia.org/wiki/Windcatcher | ||
--> | --> | ||
Revision as of 14:46, 30 June 2024
Physical mechanics of cooling
Passive cooling
Passive cooling tends to mean 'what happens with no moving parts'.
...so whatever amount of conduction, radiation, and/or convection would happen anyway.
Sometimes includes adding a fan, to add to the convection.
You're stirring the air better than just convection would, so heat transfer goes a faster than if warm air just sits around - but the difference is rarely much -- convection always does this at least a little when there is temperature difference (if you're in gravity; this is about density differences).
And you could argue that's technically active cooling (because you're adding work, so using energy), but intuitively it feels like it hardly qualifies.
On the technical side
This tends to mean
- conduction - a good conductor spreading heat throughout
- if any cooling happens, conduction's spreading brings the whole down
- radiation - thermal radiation means movement of charges in materials (anything above 0 K) is radiated as EM at the surface
- (black-body radiation can be seen as a "thermal radiation's real-world math becomes easier if we make some assumptions like that it's not really interacting in other ways")
- convection - fluid flow, in this context often
- air,
- flow caused by heat changing temperatures and densities
- that flow assisting better heat interchange with that fluid, because warmer air moving up tends to draws in colder air from the sides (which technically is an effect that needs gravity)
In practice there's more than one of these happening, but often one that counts for most exchange.